This invention relates to a method for the control of the supplied air/fuel ratio of an internal combustion engine with a catalytic converter which is located in the exhaust gas line, with an integrated oxygen reservoir.
Generally the air/fuel ratio which is supplied to an internal combustion engine is easily controlled such that a constant lambda value of approximately 1 is maintained in order to convert the emissions which occur in the exhaust gas specifically hydrocarbon and carbon monoxide on the one hand and nitrogen oxides on the other, at any time with good efficiency. This constant lambda control is however not always optimum since the exhaust gas composition can change greatly, especially in transient operation of the internal combustion engine.
Document DE 198 11 257 A1 discloses a process for controlling the exhaust gas aftertreatment of a DI-spark ignition and lean engine, for determining the charging state of the nitrogen oxide reservoir of a catalytic converter the exhaust gas temperature being measured, which together with the other parameters of engine operation, such as for example the transpired time since switching to lean operation, the oxygen content of exhaust gas and the torque fluctuation of the engine, constitutes a measure for the degree of charging of the nitrogen oxide reservoir.
Document DE 103 40 633 A1 describes an exhaust gas emission control means for an internal combustion engine with a three-way catalytic converter and an air/fuel variation element. There the air/fuel ratio is forcibly changed between rich and lean depending on the amount of carbon monoxide stored in the three-way catalytic converter.
Document DE 101 03 772 A1 shows a process for operating a three-way catalytic converter with an oxygen reservoir, the air/fuel mixture which is supplied to the internal combustion engine being controlled such that the oxygen reservoir of the catalytic converter is kept in a middle setpoint range between a minimum degree of filling and a maximum degree of filling. The drift of the degree of filling can be checked there by making the air/fuel mixture richer and leaner in alternation.